1. Field of the Invention
The present invention relates to a method of securing freight containers on a deck of a large ship such that the freight containers can effectively withstand external force, such as inclined loads and horizontal loads, generated by rolling movement of the ship, thus ensuring safe container transportation, and increasing the effective load of the freight containers, and a spring lashing bar, a space adjuster and a securing system used in the method.
2. Description of the Related Art
Generally, freight containers to be stacked on decks of ships are box type cases for efficiently and economically receiving and transporting cargo. The freight containers have a standardized width of 8 feet. Furthermore, the freight containers typically have lengths of 20 feet or 40 feet and heights of 8 feet, 8.5 feet or 9.5 feet.
Such a freight container makes it possible to conveniently transport special cargo as well as general goods without requiring a separate outer packing process, thus reducing working time and expense. Furthermore, the freight container can prevent incidents such as the damage, loss or theft of cargo. In addition, in the case of the use of the freight container, work of loading or unloading freight containers on a freight train, a freight car or a ship can be mechanized, so that there is an advantage in that the time required for the loading and unloading operation is markedly reduced.
To benefit from these advantages, recently, large ships have been used to transport a large number of freight containers to realize a reduction in transportation costs, for example, six or more tiers of containers are stacked on the deck of the ship to load several thousand freight containers on the deck of the container ship.
Furthermore, because of an increase in size of ships and the stability thereof, eight or more tiers of containers can be loaded on a deck. However, because the securing force and the self-strength of the containers are insufficient, only light containers, for example, almost empty containers, are loaded on a fifth tier of container and above.
FIG. 1 is a view illustrating a method of securing freight containers on a deck of a container ship according to a typical art.
As shown in the drawing, in the case of a very large container ship, to increase the efficiency of securing freight containers, a lashing bridge 20 having a height corresponding to that of one or two tiers of containers is provided in the lateral direction of the ship. The lashing bridge 20 functions to raise the height of the container support point of the ship to respond to an increase of the number of tiers of containers.
Typically, to couple freight containers 10 on the deck with respect to the vertical direction, twistlocks 11 are coupled between the freight containers 10. Thereafter, to increase the strength of resistance against inclined loads and lateral loads, the containers 10 are fastened to the lashing bridge 20 using lashing bars 12, which are provided in an “X” shape.
However, as shown in the drawing, the X-shaped securing method can be used only with one or two tiers of containers, because of problems pertaining to the length of each securing device and the fact that the weight is proportional to the length thereof. Furthermore, although the containers are secured to a double lashing bridge 20, the securing force is not sufficient, because it depends on the thickness of the lashing bars. In addition, freight containers, which are disposed above the containers that are secured by the X-shaped securing method, are secured using only the twistlocks 11 in the vertical direction.
Furthermore, in the very large container ship, six or more tiers of freight containers can be stacked on the deck, but lower portions of a third or fourth tier of freight containers are fastened to the lashing bridge 20, and freight containers which are disposed below the third or fourth tier are secured only to each other in the vertical direction. With regard to the reason for this, the stacks of containers are stacked on a hatch cover 13, and the hatch cover 13 is movable relative to the ship body to prevent the hatch cover 13 from being affected by elastic deformation of the ship body attributable to waves of the sea, thus preventing damage to the hatch cover 13. Therefore, in the case where the freight containers 10 are secured to the lashing bridge 20 fixed to the ship body, freight containers which are disposed below the third or fourth tier must be secured only to each other in the vertical direction to have play between them and the ship body, thus coping with the deformation of the ship body.
Therefore, the lashing bars 12 must not be tied tightly. Due to this, the very large container ship which has a relatively large deformation rate may make sailing very dangerous. For example, under conditions of rough weather, such as a typhoon or rough waves, the container ship rolls severely, so that the freight containers that are stacked to a high height may be disconnected from each other by the rolling force of the ship and the lashing bar 12 may be snapped. Thus, the containers may fall into the sea. Moreover, in the case where the connection of the containers is broken in the middle portion of the stack of containers, the adjacent stack of containers and other stacks may subsequently collapse like dominoes.
In an effort to overcome the above problems, a technique was proposed in Korean Patent Registration No. 0768357, which was filed by the applicant of the present invention and entitled Method of securing freight containers. In this technique, adjacent containers of each tier can be secured to each other in the lateral direction such that they can effectively withstand inclined loads and horizontal loads generated by rolling movement and other complex movements of a ship, thus ensuring safe container transportation.
However, the above-mentioned method does not provide auxiliary equipment for securing containers on a deck, so that it is very difficult to actually use the method.